How Scot's yeast made a Belgian classic ale

At the time, I was under age - about 16 - but had just sneaked a pint of Draught Bass in a railway station bar before boarding my train home.

I had been seen in the bar by a fellow passenger, who had now entered the same compartment of the train.

He produced from his coat pocket a bottle of Bass, and started to lecture me on the relative merits of the two versions of this product.

The one with the red label was, he explained, pasteurised; the blue-label version was not. Or was it the other way round? I forget; it was 1958.

I thought my fellow passenger was, at best, mildly crackers; at worst, a potential molester of teenage boys. The odd thing is that I still recall the incident, more than 30 years later.

I don't remember the man's face, or exactly what he said, but the subject of his dissertation lodged somewhere in the back of my mind.

I wonder who he was. The natural conditioning of beer was not an issue at the time, and the term "real ale" had yet to be coined. It was a Proustian moment.

Natural conditioning of beer was still not an issue when, in 1964, I had my first bottle of Trappistenbier, in Belgium. I remember the name Trappistenbier - I think it was embossed on the bottle - but not the specific abbey.

Nor was I, at this first sampling, aware that there were six Trappist abbeys that made beer. I can be sure of the date, because I remember where I was working at the time.

In addition to its malty sweetness, fullness of body and alcoholic strength, the beer had what I now know was a yeast-bite. I began to look for abbey brews, and to visit Belgium whenever possible, enjoying the extraordinary beers and hearty food.

Only gradually did it dawn on me just how many Belgian beers were bottle conditioned. In their authentic form, some Belgian styles must be bottle conditioned. I have in mind particularly the true Gueuze, the production of which depends upon a re-fermentation in the bottle. In this respect, it resembles Champagne.

Anyone already familiar with Belgian specialities will know that natural conditioning is usually indicated on the label by the indication of "re-fermentation in the bottle." In Flemish, in de fles. In French, en bouteille.

All trappist beers, and many of their imitators, are bottle conditioned. The monks argue that Trappistenbier is an appellation of origin, and not of style, but I argue with their wisdom in taking this view.

To my mind, a combination of attributes have created, at the very least, a Trappist family of beer types, and bottle conditioning is one of them.

Another Belgian classic style that is usually bottle conditioned is the summertime Saison, about which I wrote not long ago. This style of beer has never been easy to find, and I was pleased to see Saison Regal among the products being offered by the new mail-order company, The Beer Cellar.

Of course, all bottled beers were once made in this way. Just as lager making never altogether dominated the western fringes of Europe, so filtration did not seem essential or affordable to the more rustic small brewers of Belgium.

Bottle conditioning remained much more extensive in Belgium than anywhere else.

In recent years, there has been a new appreciation of some regional specialities in Belgium itself, and the number of bottle conditioned beers has increased.

About 30 per cent of the Belgian beer market is taken up by specialities, most of them top fermenting (and therefore, in British terms, "ales"). Among those, well over half are bottle conditioned.

While Britain is the only nation with a really significant number of draught real ales, Belgium is its match in the bottled counterpart. Although Britain's cask-conditioned ales each have their own character, the Belgian bottled products offer a more colourful diversity.

I suggest this not to pit one European nation against another in these sensitive times, but in the spirit of vive La difference!

The interplay between Belgian and British brewing traditions has been wonderfully creative: the Flemish introduced hopped beer to eastern England in the 1400s and 1500s; British soldiers helped make English and Scottish-style ales popular in Belgium during two world wars.

A fascinating example of this interplay concerns one of the world's great bottle conditioned brews, Duvel.

I suppose the episode began with the foundation of the now-famous brewery in Breendonk, about half way between Brussels and Antwerp, in 1871.

In the early part of the present century, between the two world wars, the brewery established a strong relationship with one of the world's great brewing scientists, a Belgian, Jean De Clerck (1902-78).

At the time, Scotch Ales were fashionable in Belgium. McEwans were exporting a bottle-conditioned ale. De Clerck decided to "take apart" this ale, by examining its yeast.

This turned out to comprise somewhat between 10 and 20 strains. De Clerck took out the strains he considered most useful, cultured them up, and used them to ferment an experimental dark ale at the brewery in Breendonk.

When a brewery worker tasted the beer, he is said to have commented: "That is the devil of a brew!" Whether that story is true or not - and I give it the benefit of the doubt - the brewery called the beer Duvel when they decided to put it on the market. Duvel is a corruption, so to speak, of Devil in Flemish.

After the Second World War, golden lagers of the Pilsener type began to gain ground in Belgium. Most speciality brewers settled for trying to make a Pilsener.

The brewery in Breendonk did this, too, but they also had a better idea. They began to experiment with a golden version of Duvel, still as a strong, bottle-conditioned ale. Once again, Clerck was involved.

The dark Duvel was replaced by a golden product in 1970, and this gradually began to win over drinkers. I first tasted it during the 1970s, and was astonished. I had never tasted a golden beer with such an intensity and complexity of aromas and flavours.

Whatever brewers say, no beer remains unaltered over the years - at the least, changes in the available varieties of barley and hops have to be taken into account.

The makers of Duvel used to produce their own malt but no longer do. They have also carried out further selection and propagation of their "borrowed" yeast to make it precipitate better.

Has the beer improved or diminished in character? That is like trying to decide whether Muhammed Ali would have beaten Mike Tyson.

It certainly remains a remarkable beer. A malt made to an unusually pale specification is used; the starting gravity is 1056, and the hops are Saaz and Styrian Goldings.

Dextrose is added before primary fermentation, to boost alcohol and further attenuation. This effectively upgrades the original gravity to 1068.

The original McEwans symbiosis of strains has over the years been narrowed to two yeasts, and both are used in primary fermentation. The brew is divided into two separate batches, one for each yeast.

These two batches are not of equal sizes. This procedure is just one of the many peculiarities that make Duvel such a distinctive beer.

After primary fermentation comes a secondary, in different vessels, at lower temperatures, for three days. Although Duvel is an ale, it then has four weeks' lagering.

It is then filtered and given a priming of dextrose and a dosage of just one of the two original yeasts. The original gravity has at this point been boosted to the equivalent of 1073.

The brew is then bottled and kept for 10 to 14 days at 71.6F degrees for its third and final fermentation. Even then, the cycle is not over. The bottled product is kept for a further five to six weeks at 39-410C degrees to stabilise the beer. Even then, some buyers keep it a further three or four months in a cool, dark place.

Duvel is usually served chilled, at 45-46F degrees, though it also expresses its flavours well at a natural cellar temperature. It has an alcohol content of 8.5 percent by volume, and a very distinctive, delicate, fragrant, fruitiness, reminding me somewhat of Poire William, the brandy made in Alsace.

Duvel is a protected brand name of the Breendonk brewery, run by the Moortgat family. Of what style is this beer? It is a style of its own.

Belgium has many imitators, but they can make their intentions clear only by adopting similar names: Deugniet ("Rascal"), Sloeber ("Joker") ... there was one called Ketje ("Urchin") and there is another rather pointedly called Judas.

When I ask the great British brewers why they do not give more attention to bottle-conditioned ales, they say this method is too difficult, and who would drink them?

I wonder how many have tasted McEwan's yeast in its Belgian illegitimate offspring?